1. Field of the Invention
The present invention relates to an in-axle rotational speed sensor assembly for mounting to a fixed metallic (magnetic) member, such as a drive axle differential bearing adjustor, having a central opening therethrough for receipt of rotatable member, such as a shaft, the rotational speed of which is to measured.
2. Description of the Prior Art
Automated vehicular systems such as brake control systems, antilock brake systems (ABS), traction control systems, differential lock-up systems and the like which utilize rotational speed sensors to provide a control input signal, usually indicative of wheel speed, to a controller, such as a microprocessor based electronic control unit (ECU), are well known in the prior art. Examples of such systems and/or sensors may be seen by reference to U.S. Pat. Nos. RE 30,522; 3,961,215; 3,929,382, 3,556,610; 3,604,760; 4,585,280; 4,361,060; 3,768,840; 4,818,035 and 4,863,221, the disclosures of all of which are hereby incorporated by reference.
Typically, such rotational speed sensor assemblies are electromagnetic in nature and rely on the alignment of rotor teeth, or spaces between rotor teeth, rotating past a sensor to complete or break, respectively, a magnetic flux path to produce a digital or analog signal indicative of the rotational speed of the rotor.
Placement of wheel-speed sensor assemblies within the axle (i.e. "in-axle") to protect same is also known as may be seen by reference to U.S. Pat. Nos. 3,769,533; 4,724,935; 4,836,616, 4,862,025 and 4,862,028, the disclosures of which are hereby incorporated by reference.
The use of annular rotational speed sensor assemblies comprising an annular toothed stator/sensor which surrounds a rotating toothed rotor, or visa versa, is known in the prior art. Annular speed sensor assemblies are preferred over single or multiple point type sensor assemblies in certain situations as they provide a relatively high signal to noise ratio, tend to be self-compensating for run-out errors between the rotor and stator, and require little or no adjustment. Examples of wheel-end and/or in-axle annular speed sensor assemblies may be seen by reference to U.S. Pat. Nos. 4,870,911; 4,027,753 and 4,689,557, the disclosures of which are incorporated herein by reference.
The prior art in-axle wheel speed sensors, especially those designed for use with drive axles, were not totally satisfactory as they were point type not annular speed sensor assemblies and/or were not suitable for directly monitoring the speeds of both drive axle axle shafts and/or they were located at or adjacent the axle wheel ends, and not in the relatively more protected central portions adjacent the axle drive gearing.